A multi color flexographic press of the general type to which this invention relates is disclosed in U.S. Pat. No. 4,165,688, to D. R. Leanna et al. Such a press is typically employed for imprinting paper towel stock as it comes off of a parent roll in the form of a very wide web. Unlike most prior presses, wherein ink of only one color was applied to any one inking cylinder, the press of that patent has a single elongated inking cylinder which is divided along its length into several discrete sections, and a different colored ink can be applied to each such section so that a web passing through the press is imprinted with several lengthwise extending bands, each band being of a different color and having a width that substantially corresponds to the length of a consumer roll of paper towels or to a multiple of that length. When such an imprinted web is slit and rewound into consumer rolls, the resultant product can constitute rolls in the complete assortment of colors to be offered, with a like number of rolls of each color, all produced at the same time. As compared with prior printing apparatus, on which product of only one color could be run at any given time, such split-color printing greatly simplified the storage of different colored products and the selection, packaging and shipping of various colors and color assortments. Because of the efficiencies and economies that it affords, the split color press of the Leanna et al patent has had marked commercial success.
However, from time to time during the several years that such presses have been in commercial use, they have presented certain annoying problems that have somewhat diminished the advantages that they offer. In retrospect, the cause of those problems and the solution to them may appear to be rather simple, but the fact that it took several years to find the solution is testimony to the unobviousness of it. It is possible that the solution to those problems was hard to find because it required a breaking away from certain features of flexographic press arrangement that had been conventional for such a long time, and had been so consistently used as to have been accepted by those skilled in the art as necessary and inevitable.
In a flexographic press, the imprinting of the web is done by a flexible plate carried by a plate cylinder, and ink is transferred from the inking cylinder to the plate cylinder by means of an anilox or transfer cylinder that rotates between them and is in contact with both of them in an operative or press-closed condition. The web, as it moves in contact with the plate cylinder, is backed up by an impression cylinder. When the press is in open, non-printing condition, the anilox cylinder must be spaced from the plate cylinder; but the inking cylinder and the anilox cylinder, although preferably separable, should normally continue to rotate in contact with one another to prevent ink from drying on the anilox cylinder. There should also be provision for a spacing apart of the plate cylinder and the impression cylinder in the press-open condition, to permit web to be threaded between them and to facilitate changing of plates.
Heretofore it has been conventional to mount the impression cylinder for rotation at a fixed location and to arrange the other three cylinders for press-closing and press-opening motion toward and from the impression cylinder and one another. The split-color press of the Leanna et al patent followed this conventional arrangement. A first slidable support carried the plate cylinder for movement towards and from the impression cylinder and also carried a second slidable support on which the anilox cylinder was carried for movement toward and from the plate cylinder. Arms swingable on the second support carried the inking cylinder for movement toward and from the anilox cylinder. The second slidable support also carried the fountain structure that served for applying ink to the inking cylinder.
In the press of the Leanna et al patent, the inking cylinder has circumferential grooves around it at intervals along its length, to define its several sections upon which different colored inks can be applied. For each of the several sections of the inking cylinder there is an ink nozzle from which ink is applied to the section at a rate somewhat faster than it is needed. The excess ink drains off of the inking cylinder into an ink pan that underlies the inking cylinder and the anilox cylinder, for recirculation back to the nozzle. To prevent mixing of different colored inks, the ink pan is divided into separate ink compartments, one for each section of the inking cylinder, by means of ink dams or dividers. Each ink dam extends edgewise in line with one of the grooves in the inking cylinder and serves to prevent flow of ink between the sections at the opposite sides of that groove, in addition to sealing each compartment against seepage of ink into an adjoining compartment.
For preventing flow of ink between sections of the inking cylinder, each ink dam has a hole therein through which the inking cylinder extends, and, specifically, each such hole receives a reduced diameter portion of the inking cylinder that is defined by one of its circumferential grooves. Each divider also has an arcuate edge portion which lies closely adjacent to the anilox cylinder.
An important feature of the machine of the Leanna et al patent is that its dividers are not normally in actual contact with either the inking cylinder or the anilox cylinder. Instead, their edges adjacent to those cylinders are slightly spaced from them, and the thickness of each divider is somewhat less than the width of the inking cylinder groove in which it is received.
To provide an air seal between each divider and the anilox and inking cylinders, there are passages in each divider that conduct pressure air to its edge portions adjacent to those cylinders, and air flow between the cylinder and the divider repels ink from the zone near the divider.
In the press of the Leanna et al patent, the fountain structure comprising the ink nozzles, the ink pan and the ink dams was mounted on the slidable support that carried the inking cylinder and the anilox cylinder, and it moved with those cylinders during press opening and press closing.
The problem heretofore encountered with machines of this type was that from time to time one or more of the dividers would come into contact with the inking cylinder, at one side of a groove therein, and a friction due to such contact would heat the rubber inking cylinder to the point of deteriorating it and would also warp the divider or dividers, which were made of plastic.
It was recognized that the basic cause of this problem was insufficient rigidity of the fountain structure, and particularly of the ink pan and its dividers, inasmuch as contact between a divider and the inking cylinder could only result from deformation or vibration of the divider, particularly such as could occur during press-opening and press-closing, when the carriage supporting the fountain structure and the inking and anilox cylinders moved towards and from the plate cylinder. When one surface of a divider contacted the inking cylinder, pressure air acted upon its opposite surface to maintain the divider engaged with the inking cylinder, even though the divider would have resumed its proper position in the absence of the pressure air flow.
It might be supposed that the problem could have been solved by reinforcing the ink pan to stiffen it. In fact, however, the ink pan extends across the full width of a press that normally accommodates a web having a width of 60 to 120 inches. Since the ink pan has to be as compact as possible in the direction lengthwise along the web, its long, narrow shape makes for an inherent lack of rigidity. Because it is unlikely that there will be perfect balance between forces applied at its opposite ends to actuate it for press opening and press closing motion, such actuation almost inevitably tends to twist and deform the ink pan. If the movable ink pan had been reinforced to be stiff enough to ensure against contact between the dividers and the inking cylinder, it would have been too bulky for the limited space usually available for it and too heavy to be moved easily during press opening and press closing.
The movable fountain structure entailed another inconvenience, although it was not recognized as such because nothing better was known. To accommodate movement of the fountain structure, flexible drain tubes ran from the ink pan to stationary ink reservoirs, one for each ink color. For each reservoir there was an ink pump by which ink was fed back to one or more ink nozzles, again by way of flexible tubes. In order to avoid the need for a separate ink pump for each ink nozzle, the tubes that connected a given pump with two or more nozzles that emitted the same color of ink were connected by means of tee fittings. There also had to be at least one flexible tube through which pressure air for the several dividers or ink dams was brought to the fountain structure from a stationarily mounted pump or other pressure air source. All of these flexible tubes and their connections tended to create a disorderly appearance and complicated the servicing of the machine.